1. Field of the Invention
This invention relates to a machine designed for direct or indirect application of a liquid or viscid coating medium onto a moving surface; whereby, in the case of direct application, the moving surface is the outer surface of a material web such as paper or cardboard, or, in the case of indirect application, the moving surface is the outer surface of a transfer element, preferably a transfer roll capable of transferring coating medium onto the material web; and whereby the coating machine includes a discharge nozzle for the purpose of discharging coating medium onto the surface with nozzle lips that reside on the feed-side and trailing side with respect to the moving surface.
2. Description of the Related Art
Generic free-jet nozzle coating machines are known from documents DE 44 32 177 A1, EP 0 846 804 A1 and U.S. Pat. No. 5,603,767. These documents describe designs in which one of the nozzle lips is mounted rigidly, the other nozzle lip being adjustable for the purpose of varying the height of the nozzle gap. None of the disclosed free-jet nozzle coating machines allow the adjustment of the nozzle gap to occur quickly and temporarily or allow the opening thereof in such a manner to xe2x80x9cblow outxe2x80x9d contaminants which tend to lower the quality of the coating.
The present invention relates to a coating machine of the type mentioned above which provides an improved mechanism to adjust the height of the nozzle gap.
The invention comprises, in one form thereof, a coating machine of the type mentioned above, the machine including nozzle lips of which at least one of them being formed by a blade element. By applying an elastic nozzle lip, the nozzle gap can be quickly and temporarily enlarged so that the pressure of the coating medium being supplied to the nozzle gap temporarily increases. Such a pressure pulse not only widens the nozzle gap as a result of any deflection of the blade element but also loosens any contaminants and literally blows them out of the nozzle gap. After the pressure pulse has subsided, the blade element reverts to its original position and the nozzle gap reliably changes to its original height. The blade element is preferably manufactured from steel. It is also possible to use blade elements made of fiber-reinforced plastic and, in particular, blade elements made of carbon fiber-reinforced plastic (CFRP), glass fiber-reinforced plastic (GFK), or a similar material.
In a further embodiment of this invention, the coating machine incorporates a mechanism for adjusting the height of the nozzle gap. Such a mechanism permits a variation of the coating medium being applied onto the moving surface by the coating machine with respect to a unit time.
In accordance to a first embodiment, the adjusting mechanism acts upon the blade element. In accordance to a first adjustment device of this first embodiment, the blade element can be deformed or pivoted by an adjusting unit of the adjusting mechanism. More specifically, the height of the nozzle gap can either be increased or decreased by a corresponding activation of the adjusting mechanism, starting from an initial base position of the blade element which is unaffected by the adjusting mechanism.
From a design perspective, the case of increasing the height can be accomplished by holding the blade element with one of its own length-wise edges (positioned in a transverse direction) against the coating machine, the blade element being further supported at the coating machine at a position between its two length-wise edges, and by allowing the adjusting unit to act upon the blade element at a position that is located between the support position and the mounting edge, extending in a length-wise direction.
Increasing the height can be accomplished by holding one of the blade element""s own length-wise edge (positioned in a transverse direction) against the coating machine and by allowing the adjusting unit to act upon the blade element, causing it to bend at a position that is located between the length-wise mounting edge and the free length-wise edge. Alternatively, the blade element can also be mounted via a pivot bearing. The adjusting mechanism can then pivot the blade element against an opposing spring force. Alternatively, the adjusting mechanism may include two partial adjusting mechanisms that act upon the blade element in opposite directions.
If there is a preferred operating height of the nozzle gap, a mechanical stop can be provided which defines a condition of maximum deflection or pivoting movement of the blade element corresponding to the desired operating gap height. In this condition, the gap height is essentially independent from the adjusting force of the adjusting mechanism, which simplifies the control of the adjusting mechanism.
In a further embodiment of this invention, at least one safety element is provided, which works in concert with the blade element and provides a secure mounting in the appropriate mounting receptacle of the coating machine.
The adjusting unit may include, for example, at least one pivoting lever having a fulcrum arrangement. Specifically, the free end of the fulcrum arrangement acts upon the blade element, and the other free end of the fulcrum arrangement can be moved by a force-generating device having a force-generating arrangement. By applying the fulcrum arrangement, the force-generating arrangement must not be located in the immediate vicinity of the discharge nozzle, where typically not much space is available. Instead, such a force-generating arrangement can be placed in an area where space is more readily available.
A pressure hose arrangement can be used as a force-generating arrangement. Alternatively, one can also use pneumatic, hydraulic, hydro-pneumatic, electric, electrochemical, or any other applicable devices.
In yet a further embodiment, the force-generating arrangement includes a plurality of force-generating devices, allowing such forces to be distributed perpendicular to the surface. This makes it possible to adjust the height of the nozzle gap in several sections along the working width of the surface independently from one another, which allows a cross-profiling of the coating being applied onto the surface.
The pivot bearing of the fulcrum lever arrangement and/or the minimum of one force-generating device can each be mounted on a distribution pipe or a part connected to it.
An alternative adjusting methodology of the first embodiment allows the blade element to be placed in a mounting receptacle that can be adjusted by the adjusting mechanism. In this case, the mounting can be made of a joint element having cylinder segments. Specifically, the joint element is placed in a socket, which is connected to the distribution pipe or a part mounted to it. The adjusting mechanism can act upon the joint element on the side of the coating machine, for example, either on the drive side or on the guide side of the coating machine where there is sufficient room available.
In an even further embodiment of the coating of the present invention, it is also possible for the adjusting mechanism not to act upon the nozzle lip which includes the blade element but to act upon a second nozzle lip which has no blade element. A joint element, composed of cylinder segments, is part of the second nozzle lip and is movable in a socket via an adjusting mechanism, which, in turn, should be attached to the distribution pipe or a part mounted to it. Furthermore, the second nozzle lip can be an integrated element of the joint element or made as an individual piece connected to the joint element. For the latter, it is fluid-dynamically preferred for the joint element to be, in essence, tear-dropped shaped. Specifically, the area of the section which is supported by the socket has essentially the outline of a circle while the section forming the nozzle lips decreases to a sharp corner. Again, the adjusting mechanism can act upon at least one of the ends of the joint elements, either on the drive side or the guide side of the coating machine.
If both nozzle lips are part of the adjusting mechanism, the coating machine can, in accordance to the present invention, not only affect the nozzle height by a coordinated adjustment of the position of both nozzle lips but also the direction of the jet of the coating medium exiting the discharge nozzle, without having to change the position of the coating machine. This is especially advantageous because the optimum angle of the cooling medium jet with respect to the moving surface can be achieved by adjusting parts that have relatively low mass inertias and can accordingly be adjusted correspondingly fast.
The adjustment of the two nozzle lips can also be performed in a manner such that the nozzle lip formed by the blade element can be moved from an idle position to an operational position at which it shall remain during operation. For example, the blade element can be moved against a mechanical stop, as already mentioned above. The height adjustment of the nozzle gap during normal operation is accomplished by adjustment of the other nozzle lip. To xe2x80x9cflush outxe2x80x9d the nozzle gap, it is, however, possible to temporarily move the blade element from the operational position to the idle position. The widening in the nozzle height achieved through this procedure can, if so desired, be assisted by the pressure pulse generated by the widening of the nozzle gap.
In a further embodiment of this invention, the nozzle lips are formed of a minimum of two shell-like or shell shaped pieces, which together form the walling of a distribution channel located upstream of the discharge nozzle with respect to the flow of the coating medium. Such shell-like pieces are easier to manufacture using cast or extrusion manufacturing technologies rather than are profile pipes, which, in turn, also benefits the manufacturing process of the coating machine of the present invention. The two shell-like pieces can also be manufactured of fiber-reinforced plastic, i.e., carbon fiber-reinforced plastic (CFRP), or Polyvinylchloride, (PVC), especially, chlorinated Polyvinylchloride (PVC-C). They can be connected to one another simply through adhesion, bolting, or a similar method.
Additionally, the shell-like pieces can form together an equalization chamber that resides between the distribution channel and the discharge nozzle, in which the coating medium exiting the distribution channel is equalized prior to entering the nozzle gap. Attached to the shell-like pieces, receptacles or mounting arrangements can be incorporated for each respective nozzle lip.
Finally, in a further embodiment of this invention, the coating machine includes a distribution channel located upstream of the discharge nozzle with respect to the coating medium flow; an equalization chamber that resides between the distribution channel and the discharge nozzle; and a device for accommodating an insert in the transitional section between the distribution channel and the equalization chamber, the device having a plurality of openings for the coating medium exiting the distribution pipe. This insert can, in accordance to this invention, be a xe2x80x9cblending devicexe2x80x9d between the distribution channel and the equalization chamber and is designed so as to be interchangeable with an insert having a smaller or larger number of openings and/or openings with smaller or larger cross-sectional areas, in order to accommodate a variety of coating mediums with a range of viscosities.
A simplification of the coating machine construction and its components can be achieved by making the distribution pipe a separate entity from the associated carrier element or beam. This modular construction allows a relatively simple, thermally isolated attachment of the distribution pipe onto the carrier element. This avoids stresses associated with the entire apparatus, especially stresses in the distribution pipe, as a result of expansion differences between the carrier element and the distribution pipe. Different thermal expansion coefficients associated with the materials that are used for the different parts will therefore not have a negative impact on the coating quality.
Although the above embodiments are based on a free-jet coating machine that is positioned at a distance from the moving surface and is configured for applying coating medium onto the moving surface under high pressure using a free unsupported jet, the coating machine, as designed per this invention, can also be applied as a curtain coater, i.e., a coating machine with short dwell time (SDTAxe2x80x94short dwell time applicator). In the latter, the nozzle gap, delimited by the nozzle lips, forms the applicator chamber, in which the coating medium is brought into contact with the moving surface during a short residence time. With this design, the downstream nozzle lip can be designed to serve the function of applying the final metering and, if desired, of equalizing the coating medium being applied onto the surface. Alternatively, such a final metering/equalization function can be accomplished by a device that is mounted separately.
With curtain coaters, the coating medium is applied by taking advantage of gravity. This limits the amount of application so that final metering/equalization is no longer required.